1. Technical Field
The invention relates generally to inductive heating and inductive furnaces. More particularly, the invention relates to an induction furnace for melting particulate material. Specifically, the invention relates to an induction furnace for melting particulate material as the material is freely falling.
2. Background Information
The melting of granular material, powders and other particulate material presents several challenges. One of these challenges relates to the reluctance of particulate material to submerge into a molten bath of the same or similar material. A variety of factors are involved regarding this reluctance to submerge, including high surface tension of the molten bath as well as bulk density differences. Due to the tendency of particulate material to lie on the surface of the molten bath, the particulate material may be oxidized when the melting procedure takes place in an oxygen environment. In traditional induction furnaces, a meniscus is formed within the molten bath and the agitation or stirring within the molten bath helps to draw the particular material into the bath. However, the effectiveness of this agitation or stirring is marginally effective and the particulate material often remains atop the surface of the molten bath. This problem can be exacerbated if the feed rate of the particular material is too fast. In some cases, a dome of unmelted material known in the industry as a bridge may form atop the molten bath which can result in the superheating of the bath and potentially the melting of the containing crucible.
One partial solution to the problems associated with the addition of powders and other particulate material has been to form briquettes from the particulate material for use with induction, plasma or arc-type furnaces. One problem with the use of such briquettes is premature dissociation. In addition, some briquettes use binders which are a potential source of contamination in certain high purity materials and also give off gases which must be handled. The use of briquettes thus requires additional equipment, material handling and involves greater cost.
Another common problem with traditional melting methods is the use of particulate material which is coated with an oxide or the like. These oxides and the like create a buildup of a layer of slag on the surface of the molten bath. This slag layer also prevents additional particulate material from being absorbed into the molten bath.
There are other drawbacks related to traditional furnaces. Generally, such furnaces typically melt in batches as opposed to having the ability to provide a continuous melting process. In addition, many of these furnaces are physically large and must be mounted on floors or large platforms. The transfer of molten material from the furnace is typically done by a pour spout or an overflow method. Due to the weight of the crucibles and molten material, chain hoists or a hydraulically powered mechanism may be required to lift or tilt the crucible in order to pour the molten material out. In addition, these furnaces often pour the molten material into a secondary furnace or tundish. This may require the use of a launder as an intermediate structure involved in the transfer of the molten material. Thus, these and other types of furnaces require additional structural components which add to the cost of the process. Attempts to create a bottom pour mechanism have met with varying degrees of success and so the pouring of molten material remains an area for improvement.